Important trimming question...

Mush

Mush

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I load 338 LM using Lapua cases.
I only neck size and bump shoulder every 3 firing.
When do I trim ?
Just after firing or do I have to neck size before ?
Do I have to bump shoulder before trimming ?

Mush
 
I'd case size your new brass but unfired Lapua should not need any sizing.

For fired brass, I would at least neck size after every firing and shoulder bump after 3 firings. Personally I full-size after each firing.
Remember that when you are shoulder bumping or full-length resizing, your die is pushing the shoulder back towards the base of the cartridge. This will cause the neck to lengthen the same distance that you are moving the shoulder. So trimming may be needed after a few bumps (or not) depending on how far you move the neck. A case gauge is useful for quickly evaluating the need to trim.
 
OldDude said:
I always measure case length and trim if necessary after re-sizing......
Click to expand...

Ok after resizing.
But after neck sizing or full lenght resizing ?
As I understand, both process makes the brass flow upward.

Mush
 
Size and measure and see what you discover.

Try some neck sizing and some FL, compare your findings.

Personally, I always trim after sizing, the neck is also proper diameter at this time which fits my pilot on the trimming tool.
 
For my 338 LM I do a partial full length resize setting the shoulder back about 0.002" then measure the OAL to see if I need to trim
 
OP.........buy yourself a good set of dial gauge calipers, learn how to use them and then read the section in your loading manuals on trimming brass. It is the same for all cartridges, when they approach SAAMI max, take .010" off..........It matters not what you do to the cases, neck size, full length size or partial size, trimming is just part of the process and some cartridges are more prone to growth than others.
 
Why don't you just look up the trim to length in the reloading manual and do that. All this 3 times stuff is forgetting that no one knows the brass you use or the loads employed. You brass may stretch more or less that others.

If it is too long trim. If not leave. Right outta the manual.
 
Pr589 said:
I'd case size your new brass but unfired Lapua should not need any sizing.

For fired brass, I would at least neck size after every firing and shoulder bump after 3 firings. Personally I full-size after each firing.
Remember that when you are shoulder bumping or full-length resizing, your die is pushing the shoulder back towards the base of the cartridge. This will cause the neck to lengthen the same distance that you are moving the shoulder. So trimming may be needed after a few bumps (or not) depending on how far you move the neck. A case gauge is useful for quickly evaluating the need to trim.
Click to expand...

You always need to FL size and trim new brass, Lapua included. My 9.3x62 brass had lots of dented case mouths that had to be taken care of. And why wouldn't you start with brass that you knew was 100% uniform? Just makes more sense if you're trying to turn out quality handloads.
 
Like curseyou says, you trim when your case get longer than the max case length given in your manual.
You likely don't need to 'bump' anything every three times either. That gets done when the cases get hard to chamber.
 
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